Method for producing cast molded parts as well as cast molded parts produced according to the method

ABSTRACT

The invention relates to a method for the production of castings made of a copper alloy comprising silicon, nickel, chromium, and zirconium, and also inter-metal primary phases, wherein an ingot is drawn by means of hot forming in only one direction at a ratio of at least 4:1, wherein a casting surface of a casting produced from the drawn ingot, said surface coming into contact with a metal melt, is substantially selected perpendicular to the drawing direction of the ingot. A casting produced in this manner is characterized by high wear resistance and increased service life, particularly when used as a block of a side bank of a double strip casting system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing cast moldedparts from a copper alloy containing silicon, nickel, chromium andzirconium as well as intermetallic primary phases. Furthermore, thepresent invention relates to cast molded parts produced according tothis method.

2. Description of Related Art

Published European patent document EP 0 346 645 B1 describes the use ofa curable copper alloy made up of 1.6 to 2.4% nickel, 0.5 to 0.8%silicon, 0.01 to 0.20% zirconium, the remainder being copper includingproduction-related impurities and the usual processing additives, asmaterial for producing cast molded parts, which are subjected topermanently changing thermal stressing during the casting process, inparticular in the form of blocks for side dams of twin-belt castingsystems. The capacity of twin-belt casting system depends considerablyon the proper functioning of the side dam chain formed by blocks. Forexample, the blocks must have the highest possible thermal conductivityso that the melting or solidification heat is able to be dissipated asquickly as possible. In order to avoid premature wear of the side edgesof the blocks due to mechanical stressing, which leads to the formationof gaps between the blocks and then to the penetration of the moltenmass into this gap, the material must exhibit not only high hardness andtensile strength but also a small grain size.

Finally, optimum fatigue behavior of the material is of the mostdecisive significance, which will ensure that the thermal stressesarising during cooling of the blocks after they leave the casting linedo not lead to cracking of the blocks at the corners of the T grooveincorporated for the accommodation of the steel band. If such crackscaused by thermal shock do appear, the respective form block will fallout of the chain after even a short period of time and molten metal isable to run uncontrollably from the casting form cavity and damage partsof the installation. An exchange of the faulty block requires the systemto be stopped and the casting operation to be interrupted.

A testing method in which the blocks are subjected to heat treatment fortwo hours at 500° C. and are subsequently quenched in water at 20 to 25°C., has proved useful for checking the tendency to crack. Even if thisthermal shock test is repeated several times, no cracks must appear inthe region of the T groove in the case of a suitable material.

The zirconium-containing, curable CuNiSiCr alloy described in EP 0 346645 B1 is extremely suitable for blocks in side dams of twin-beltcasting systems. The addition of chromium increases the conductivity ofthe material. The Fe addition restricts the increase in grain sizeduring the solutionizing treatment without adversely affecting the otherproperties of the material.

It is known that intermetallic primary phases occur in the structure ofthe chromium- and zirconium-containing material, which crystallize inhypoeutectic manner, i.e., with an inhomogeneous distribution, duringthe solidification of the melt. For method-related reasons, theseCrSi-containing and NiZr-containing phases already occur in the castround ingots that are used as starting material for the production ofblocks for the side dams of twin-belt casting systems. In order toadjust a fine-grained structure and to achieve the required hardness andelectrical conductivity, the molten material is usually formed whilestill warm, employing conventional deformation processes such asextrusion, forging or rolling, and subsequently solutionized and cured;in the process, the eutectic, inhomogeneous distribution of theintermetallic primary phases of the casting state are more or lessdestroyed, and the primary phases are aligned in the form of bands inthe main deformation direction. When the blocks are produced in theconventional manner from extruded or hot-rolled rods, then a relativelyunevenly distributed primary-phase arrangement in the casting surface ofthe blocks featuring a distinctly banded orientation is present. Duringthe forging of plates from an unworked cast piece, the net-likedistribution of the intermetallic primary phases of the casting state isusually removed only insufficiently since the overall deformation degreeis limited, and the plate is formed in approximately the same way in thelongitudinal and the transverse direction.

SUMMARY OF THE INVENTION

Using this as the starting point, the present invention is based on theobjective of optimizing a method for producing cast molded parts, inparticular for producing blocks for side dams of twin-band castingsystems, such that the wear of the casting surfaces coming into contactwith molten metal sets in later and progresses more slowly, so that acast metal band featuring a perfect surface quality is able to beproduced over a longer period of production using the cast molded parts.Furthermore, a cast molded part having improved properties is to beprovided.

The invention provides a method for producing cast molded parts madefrom a copper alloy containing at least one alloy element from each ofthe groups a) and b), group a) including nickel and cobalt, and group b)including chromium, zirconium, beryllium and silicon, as well asintermetallic primary phases, a cast ingot being ironed by hotdeformation in only one direction, at a ratio of at least 4:1; an angleof 90°±10° relative to the ironing direction of the cast ingot beingselected for a casting surface, which comes into contact with the moltenmetal, of a cast molded part that is produced from the ironed castingot.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a micrograph of a cast round ingot which can be used as astarting material for the production of cast molded parts of side damsof a twin-belt casting system.

FIG. 2 shows the distribution of the intermetallic primary phases of acast ingot that already underwent hot deformation, and thus themicrograph in the region of the casting surface of a later castcomponent.

FIG. 3 shows a micrograph perpendicular to the casting surface and thusperpendicular to the micrograph of FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

The objective underlying the present invention is achieved in thatselective hot deformation is used to orient the intermetallic primaryphases included in the copper alloy in such a way that a castingsurface, which comes into contact with the molten metal, of a castmolded part that is produced from the ironed cast ingot is selected tobe at an angle of 90°±10°, i.e., essentially perpendicular, to theironing direction of the cast ingot. “Essentially perpendicular” as usedin the following text means an angle of 90±10° relative to the ironingdirection of the cast ingot. Perpendicular denotes an angle of 90°.

The essential aspect in this procedure is that the hot shaping of thecast ingot not only produces the fine-grained structurerecrystallization of the originally coarse-grained casting structure,but also a distinct fiber orientation featuring a reduction in size andan alignment of the intermetallic primary phases in line with thesefibers. In this context it is important that if possible, the fiberorientation has fine and evenly distributed primary phases, which in theframework of the present invention is achieved in that the ironing byhot forming takes place in only a single direction, the cast ingot beingironed at a ratio of at least 4:1, preferably more than 7:1. The hotforming may be performed employing methods such as forging or hotrolling. In contrast, a sweeping overall deformation of at least 4:1 orpreferably of at least 7:1, in different directions, does not lead tothe fiber flow aimed for according to the present invention.

Another important method feature is that the cast molded parts producedfrom the ironed cast ingot have a casting surface which comes intocontact with the molten metal that is selected essentially perpendicular(=90±10°), preferably precisely perpendicular, to the ironing direction.Only in this case will the wear of the cast surfaces be reducedsignificantly, thereby making it possible to produce a cast metal bandhaving perfect surface quality over a longer period of production.

Because of the orientation of the fibers, the intermetallic primaryphases in the casting surface essentially manifest themselves only inthe form of evenly distributed dots. It is considered useful if thequantitative proportion of the intermetallic primary phases, cut in amicrograph, between the casting surface and the sides of the ironedcasting ingot standing perpendicular to the casting surface is set to begreater than 1.5:1. This means that at least 50% more intermetallicprimary phases are cut in the casting surface, or in a plane runningessentially perpendicular to the ironing direction, than in a side orplane perpendicular to the casting surface.

The quantitative proportion of the cut intermetallic primary phasesadjusted in this manner, in combination with the orientation of thecasting surface leads to cast molded parts featuring an optimizedapplication behavior since the introduction of fissures and the spreadof fissures in the casting surface is inhibited. This reduces the wearof the cast molded parts during use since the fissure spread proceedsmore slowly, which contributes to an increase in service life. Theresistance to the formation of fatigue fissures is markedly higher incomparison with cast molded parts in which the intermetallic primaryphases are essentially non-aligned.

The cast molded part produced according to the method of the presentinvention has a fiber flow that causes the intermetallic primary phasesto be arranged in fibers or bands as well. The average length of aprimary phase lying in a plane is able to be measured. It is consideredadvantageous if the ratio between the average length of a band lying inthe plane of the casting surface, and the average length of a band thatruns essentially perpendicular (=90±)10°, preferably preciselyperpendicular, to the casting surface is less than 3:10. In other words,there are bands of intermetallic primary phases in the casting surfacewhose length corresponds to maximally 30% of the length of a band of anintermetallic primary phase that runs essentially or preciselyperpendicular to the casting surface.

The cast molded part according to the present invention is made of acurable copper alloy, which for this purpose contains alloy componentswhich precipitate as intermetallic phases. The curable copper alloypreferably contains nickel, which may be at least partially replaced bycobalt. In addition, the alloy contains at least one of the followingalloy elements: chromium, zirconium, beryllium, silicon.

The finished cast molded part is characterized by excellent materialproperties tailored to the specific application case, i.e., especiallyby a tensile strength of at least 600 MPa at a room temperature of 20°C., and a tensile strength of at least 350 MPa at a temperature of 500°C.

In the cured state, the copper alloy has an 0.2% yield strength of atleast 470 MPA at 20° C., a breaking elongation A₅ of at least 15%, ahardness of at least 190 HV10 and an electric conductivity of at least40% IACS (IACS=International Annealed Copper Standard, electricconductivity in comparison with copper=100%) at 20° C. The electricconductivity preferably amounts to at least 45%.

The cured copper alloy is to feature a grain size of maximally 130 μmmeasured according to ASTM E 112. The U.S. ASTM E 112 standard (AmericanSociety for Testing and Materials) is a standard testing method fordetermining the average grain size.

FIG. 1 shows a micrograph of a cast round ingot, which is used asstarting material for the production of cast molded parts of side damsof a twin-belt casting system. It involves the typical cast structure ofa CuNiSiCrZr alloy having CrSi-containing or NiZr-containingintermetallic primary phases in a eutectic arrangement. Subsequently,deformation methods such as extrusion, forging or rolling are used todeform the material in order to adjust a fine-grained structure and toachieve the required hardness and electrical conductivity; then, thematerial is subjected to a solutionizing treatment and cured, so that achange occurs in the eutectic, inhomogeneous distribution of theintermetallic primary phases.

If the unworked cast piece shown in FIG. 1, which has a net-likedistribution of the intermetallic primary phases, is deformed to thesame extent both in the longitudinal and the transverse direction, thenthe phase orientation does not change in the desired manner.

In contrast, FIG. 2 shows the distribution of the intermetallic primaryphases of a cast ingot that already underwent hot deformation, and thusthe micrograph in the region of the casting surface of a later castcomponent. It can be seen quite clearly that the intermetallic primaryphases are very fine and evenly distributed. The fiber orientation, orthe orientation of the intermetallic primary phases, runs perpendicularto the casting surface, so that the cut primary phases appear as dots inthis figure.

The number of cut primary phases is approximately 1.7 as high as in FIG.3, which shows a micrograph perpendicular to the casting surface andthus perpendicular to the micrograph of FIG. 2. While the phase bandsare discernible only in rudimentary form in FIG. 2 and have a maximumlength of approximately 100 μm, a much higher number of primary phasebands can be seen in FIG. 3, the phase band lengths ranging from 100 to400 μm, and partially amounting to more than 400 μm. The following tableillustrates the mechanical properties and the fatigue resistance of castmolded parts made from CuNiSiCrZr alloys according to the method of thepresent invention.

Response Following El. Fatigue % Thermo- R_(m) R_(p0.2) Hardness Cond.R_(m) Service Shock Grain Size Exemplary MPa MPa A_(s) % HV10 % IACS MPaLife Testing ASTM E112 Embodiment Testing temp. 20° C. Testing temp.500° C. μm A (R = 5.3:1) Fiber 637 514 17 210 51.4 381 117 fissure-45-65 perpendicular free to casting surface (according to the invention)Fiber parallel 625 502 15.5 210 51.6 371 100 fissure- 45-65 to castingfree surface (not standard implementation according to the invention) B(R = 7.3:1) Fiber 640 518 16 212 51.4 402 126 fissure- 30-45perpendicular free to casting surface (according to the invention) Fiberparallel 635 513 15 216 51.2 371 100 fissure- 30-45 to casting freedirection (not standard implementation according to the invention)

Exemplary embodiment A is based on an alloy having the followingcomposition in weight-%:

 2.1% Ni 0.62% Si 0.30% Cr 0.15% Fe remainder = copper, includingunavoidable impurities.

This alloy was smelted in an induction crucible furnace and cast in theform of a round ingot using an extrusion method. The round ingot waspreheaded in a forging press within a temperature range between 950° C.and 750° C. and then shaped into a cuboid. The cuboid was subsequentlyforged into a plate in the longitudinal direction. This blocked platewas then rolled to its final dimensions in a hot rolling mill between950° C. and 800° C. The overall deformation ratio R in the longitudinaldirection, based on the preheaded length and ending with the completelyrolled plate length, amounted to 5.3:1. The plate was subsequentlysolution-annealed and cured. The cooling following the curing wasperformed in a kiln at a defined cooling rate. Subsequently, the platewas sawed into horizontal strips, and these strips were then used toproduce cast molded parts, also referred to as dam blocks, having thedimensions of 70 mm×50 mm×40 mm.

As an alternative, the cast molded parts having dimensions of 60 mm×50mm×40 mm or 50 mm×50 mm×40 mm may be obtained in the same manner aswell. Preferably, the casting surfaces of the cast molded parts inessence come to lie exactly perpendicular to the longitudinal directionof the plate, and thus preferably in essence also exactly perpendicularto the ironing direction of the deformed cast ingot or the fiberalignment.

The table reproduces the mechanical/technical properties and also thefatigue resistance of formed molded parts thus produced, in comparisonwith cast molded parts whose fibers lie parallel to the casting surfaceand which have not been subjected to a preferred deformation at a ratioof at least 4:1. In laboratory testing, the cast molded parts producedaccording to the present invention, having an alignment of theintermetallic phases that runs perpendicular to the casting surface,exhibit a fatigue resistance that is 17% higher than that of cast moldedparts whose fiber position runs parallel to the casting surface.

Exemplary embodiment B is based on an alloy having the followingcomposition:

 2.2% Ni 0.60% Si 0.33% Cr 0.12% Fe remainder = copper, includingunavoidable impurities.

This alloy, too, was smelted in an induction crucible furnace and castin the form of a round ingot using an extrusion method. Then, the roundingot was rolled into a plate on a hot rolling mill between 950° C. and800° C. The overall deformation ratio R in the longitudinal directionrelative to the starting length of the cast ingot amounts to 7.4:1, andthus corresponds to the preferred specification according to the presentinvention of at least 7:1.

The further treatment of the hot-rolled plate and the removal of thecast molded parts is performed in the manner shown in exemplaryembodiment A.

Table 1 once again reproduces the hardness properties of the cast moldedparts having primary phases that run perpendicular to the ironingdirection, in comparison with cast molded parts whose intermetallicprimary phases run parallel to the casting direction.

In laboratory testing, the cast molded parts produced according to thepresent invention and shown in exemplary embodiment B exhibit a fatigueresistance that is even 26% higher in comparison with cast molded partshaving a fiber alignment parallel to the casting surface, the mechanicalproperties being approximately equal.

The exemplary embodiments illustrate that the cast molded parts producedaccording to the present invention provide a fatigue behavior of thecasting surface that it 17 to 26% better than comparable cast moldedparts having a fiber and phase alignment parallel to the casting surfaceor having no preferred orientation.

1-16. (canceled)
 17. A method for producing a cast molded part from acopper alloy containing at least one alloy element selected from thegroup consisting of nickel and cobalt and at least one alloy elementselected from the group consisting of chromium, zirconium, beryllium andsilicon, and having intermetallic primary phases, comprising: providinga cast ingot which is ironed by hot deformation in only one direction,at a ratio of at least 4:1, the cast ingot having a casting surfacewhich is essentially perpendicular to the ironing direction of the castingot, and bringing the copper alloy, in a molten state, into contactwith the casting surface of the ironed cast ingot so as to produce acast molded part from the copper alloy.
 18. The method as recited inclaim 17, wherein a quantitative proportion of the intermetallic primaryphases, cut in a micrograph, between the casting surface and sides ofthe ironed casting ingot standing at an angle essentially perpendicularto the casting surface is set to be greater than 1.5:1.
 19. The methodas recited in claim 17, wherein the cast ingot is ironed by hot rollingin only one direction, at a ratio of at least 7:1.
 20. The method asrecited in claim 18, wherein the cast ingot is ironed by hot rolling inonly one direction, at a ratio of at least 7:1.
 21. The method asrecited in claim 17, wherein the cast ingot is ironed by hot forging.22. The method as recited in claim 17, wherein the cast ingot is ironedby hot rolling.
 23. A cast molded part produced according to the methodas recited in claim
 17. 24. The cast molded part as recited in claim 23,wherein a quantitative proportion of the intermetallic primary phases,cut in a micrograph, between the casting surface and sides of the ironedcasting ingot standing at an angle essentially perpendicular to thecasting surface is set to be greater than 1.5:1.
 25. The cast moldedpart as recited in claim 23, wherein the intermetallic primary phasesare arranged in bands, and a ratio between an average length of a bandlying in a plane of the casting surface and an average length of a bandthat runs at an angle essentially perpendicular to the casting surfaceis less than 3:10.
 26. The cast molded part as recited in claim 23,wherein the copper alloy when cured has a tensile strength of at least600 MPa at 20° C., and a tensile strength of at least 350 MPa at 500° C.27. The cast molded part as recited in claim 23, wherein the copperalloy when cured has an 0.2% yield strength of at least 470 MPa at 20°C.
 28. The cast molded part as recited in claim 23, wherein the copperalloy when cured has an A₅ breaking elongation of at least 15% at 20° C.29. The cast molded part as recited in claim 23, wherein the copperalloy has a hardness of at least 190 HV10 at 20° C.
 30. The cast moldedpart as recited in claim 23, wherein the copper alloy has an electricconductivity of at least 40% IACS at 20° C.
 31. The cast molded part asrecited in claim 23, wherein the copper alloy has an electricconductivity of at least 45% IACS at 20° C.
 32. The cast molded part asrecited in claim 23, wherein the cured copper alloy has a grain size ofmaximally 130 μm measured according to ASTM E
 112. 33. A block for sidedams of a twin-belt casting system produced according to the method asrecited in claim 17.